Bethe-Salpeter study of radially excited vector quarkonia

We solve the Bethe-Salpeter equation (BSE) for a system of a heavy quark-antiquark pair interacting with a Poincare invariant generalization of screened linear confining potential. In order to get reliable description the Lorentz scalar confining interaction is complemented by the effective one gluon exchange. Within presented model we reasonably reproduce all known radial excitations of the vector charmonia. We have found that $J/\Psi$ is the only charmonium left bellow naive quark-antiquark threshold $2m_c$, while the all excited states are situated above this threshold. We develop a method which is enable to provide solution of full four dimensional BSE for the all excited states. We discuss the consequences of the use of the free propagators for calculation of excited states above the threshold. The Bethe-Salpeter string breaking scale $\mu\simeq 350MeV$ appears to be relatively larger then the one defined in various potential models $\mu\simeq 150MeV$.Comment: typos and grammar correcte

Retardation effects in the rotating string model

A new method to study the retardation effects in mesons is presented. Inspired from the covariant oscillator quark model, it is applied to the rotating string model in which a non zero value is allowed for the relative time between the quark and the antiquark. This approach leads to a retardation term which behaves as a perturbation of the meson mass operator. It is shown that this term preserves the Regge trajectories for light mesons, and that a satisfactory agreement with the experimental data can be obtained if the quark self-energy contribution is added. The consequences of the retardation on the Coulomb interaction and the wave function are also analyzed.Comment: 4 figure

Quark self-energy and relativistic flux tube model

The contribution of the quark self energy to the meson masses is studied in the framework of the relativistic flux tube model. The equivalence between this phenomenological model and the more QCD based rotating string Hamiltonian is used as a guide to perform the calculations. It is shown that the addition of the quark self energy to the relativistic flux tube model preserves the linearity of the Regge trajectories. But, following the definition taken for the constituent quark masses, the Regge slope is preserved or decreased. In this last case, experimental data can only by reproduced by using a string tension around 0.245 GeV$^2$. Two procedures are also studied to treat the pure flux tube contribution as a perturbation of a spinless Salpeter Hamiltonian.Comment: 4 figures, 4 table

Role of Fermion Exchanges in Statistical Signatures of Composite Bosons

We study statistical signatures of composite bosons made of two fermions using a new many-body approach. Extending number-states to composite bosons, two-particle correlations as well as the dispersion of the probability distribution are analyzed. We show that the particle composite nature reduces the anti-bunching effect predicted for elementary bosons. Furthermore, the probability distribution exhibits a dispersion which is greater for composite bosons than for elementary bosons. This dispersion corresponds to the one of sub-Poissonian processes, as for a quantum state, but, unlike its elementary boson counterpart, it is not minimum. In general, our work shows that it is necessary to take into account the Pauli exclusion principle which takes place between fermionic components of composite bosons - along the line here used - to possibly extract statistical properties in a precise way.Comment: 14 page